The present invention relates generally to vibration-damping structural components, and more particularly to such components which have improved resistance to flexural modes of vibration.
Various load-bearing systems and structures, such as aircraft, experience vibrations during use which cause them to suffer from high cyclic and resonant fatigue and reduced service life. Devices for reducing such vibrations combine alternating layers of stiffness and damping materials in a single composite. Under bending or flexural loads, the stiffness layers deform, shearing the damping layers, which, because of their viscosity, convert the shear strain energy into heat, thereby dissipating the vibrational energy. In vibrational environments structures employing these composites have operational characteristics, durability, and service life that far exceed those of components based solely on stiffness materials. In some cases, these layered composites are fixed to the surface of a pre-existing base structure subject to vibrations. The damping layer is generally bonded to the base structure itself and a constraining cover layer of stiffness material is bonded to the damping layer. Another such device includes an additional stand-off layer between the base structure and the damping layer to remove the damping layer further from the neutral axis, which is within the base structure. The stand-off layer, which has a discontinuous surface interfacing the damping layer, stretches and therefore shears the damping layer on its interfacing surface. The constraining stiffness layer is bonded directly to the damping layer.
In other cases, the structure itself is made of a vibration-damping layered composite. An example of such a composite structure is a planar lamination of stiffness and damping layers such as a sandwich construction, which has two load-bearing layers of stiffness material and a layer of viscoelastic damping material sandwiched therebetween. Attempts are on-going to increase the damping capability of these sandwich constructions by increasing the rate or amount of shear straining in the damping layer thereof. In some applications, such as in aircraft, weight is a factor in the design of these components as well.